In prior art nonaqueous dispersion polymerization systems, an organic medium is utilized having poor solvent properties for the polymer being produced. A dispersing agent is utilized in the organic medium in order to disperse the polymer being formed throughout the medium. These dispersing agents are generally polymeric materials such as block copolymers, random copolymers, or homopolymers as described in U.S. Pat. Nos. 4,098,980 and 4,452,960.
Styrene-butadiene rubbers (SBR) are elastomers and have generally been prepared in solvents in which SBR is soluble. Only SBR's having a styrene content of less than 35% are soluble in hexane or linear aliphatic solvents. SBR having a styrene content greater than 35% have been polymerized in aromatic or cycloaliphatic solvents via solution polymerization. These polymers are not completely insoluble in the linear alkane solvents, and in fact are highly swollen in these solvents. A process for the nonaqueous dispersion polymerization of styrene and butadiene monomers into a SBR having a styrene content greater than 35% would be highly desirable.
It is an object of the present invention to provide a dispersing agent and anionic initiation system to promote the random polymerization of styrene and butadiene monomers in a nonaqueous dispersion into SBR having 35 to 70% by weight of styrene.
Such a nonaqueous dispersion polymerization process offers many advantages over solution polymerization processes including improved heat transfer, energy savings, higher polymer concentrations in the reaction medium, increased production capacity, and very high molecular weight polymers can be produced.